Sildenafil is the main component of Intagra. Sildenafil affects the response to sexual stimulation. It acts by enhancing smooth muscle relaxation using nitric oxide, a chemical that is normally released in response to sexual stimulation. This smooth muscle relaxation allows increased blood flow into certain areas of the penis, which leads to an erection. Sildenafil is applied for the treatment of erectile dysfunction (impotence) in men and pulmonary arterial hypertension. Sildenafil may also be used for other purposes not listed above.